Containers for storing e.g. food products require a tight seal in order to be leak-tight or hermetic for hygienic or shelf-life reasons. One way of tightly sealing containers filled with powder or other food products is to bond or seal a membrane to the inner walls or to an edge or lip extending around the opening of the container. Such membranes are often arranged so that they may be easily removed from the container by a tearing force applied by the user, and the membranes are hence often provided with pull-tabs that extend from an end region thereof and that are easy to grip. U.S. Pat. No. 8,225,954 describes a sealing membrane comprising such a pull-tab.
Containers provided with sealing membranes are commonly provided with an outer lid of stiffer material e.g. made of cardboard or plastic material, such that the outer lid protects the sealing membrane as well as the pull-tab from punctures or ruptures. The outer lid is commonly arranged onto the container after the sealing membrane is applied. The pull-tab may be impacted in a non-desirable way by the outer lid as the outer lid is positioned at the opening of the container. To avoid this, the extending pull-tab may be pre-bent or pre-folded before the outer lid is applied to the container.
U.S. Pat. No. 4,122,790 describe a container with a stiff outer lid and a pre-bent pull-tab. The sealing membrane is severed by punching means from a transversely travelling web material during the manufacturing process. The membrane is sealed to the edge of the opening of the container and the pull-tab, extending from the sealing membrane, is subsequently laterally bent along the edge of the container before the outer lid is applied to the container.
Due to the small size of the pull-tab, the production speed and the difficulties in controlling the exact position of the container, it is generally a challenge to provide equipment that pre-bends or pre-folds the pull-tab in a desired and consistent way. Usually, a rod or plate is used to bend the pull-tab when the container passes the rod/plate in the production line, or the outer lid is used to bend the pull-tab when applied onto the container. This leads normally to an uncontrolled bending of the pull-tab, which in turn may lead to folding errors or collapsing of the pull-tab such that it becomes difficult to grip. Thereby, the tear-off mechanism of the membrane is affected, and the user-friendliness of the membrane is consequently reduced.
Additional steps during or after the manufacturing process to achieve a proper shaping of the pull-tab have been proposed but makes the manufacturing more costly.
There is thus a need for improvements that facilitates proper shaping/bending of sealing membrane pull-tabs in the production of containers with such membranes.